Many of the chemicals used in manufacturing integrated circuits, photomasks, and other devices with very small structures are corrosive, toxic and expensive. One example is photoresist, which is used in photolithographic processes. In such applications, both the rate and amount of a chemical in liquid phase—also referred to as process fluid or “chemistry”—that is dispensed onto a substrate must be very accurately controlled to ensure uniform application of the chemical and to avoid waste and unnecessary consumption. Furthermore, purity of the process fluid is often critical. Even the smallest foreign particles contaminating a process fluid cause defects in the very small structures formed during such processes. The process fluid must, therefore, be handled by a dispensing system in a manner that avoids contamination. See, for example, Semiconductor Equipment and Material International, “SEMI E49.2-0298 Guide for High Purity Deionized Water and Chemical Distribution Systems in Semiconductor Manufacturing Equipment” (1998). Improper handling can also result in introduction of gas bubbles and damage the chemistry. For these reasons, specialized systems are required for storing and metering fluids in photolithography and other processes used in fabrication of devices with very small structures.
Chemical distribution systems for these types of applications therefore must employ a mechanism for pumping process fluid in a way that permits finely controlled metering of the fluid and avoids contaminating and/or reacting with the process fluid. Generally, a pump pressurizes process fluid in a line to a dispense point. The fluid is drawn from a source that stores the fluid, such as a bottle or other container. The dispense point can be a small nozzle or other opening. The line from the pump to a dispense point on a manufacturing line is opened and closed with a valve. The valve can be placed at the dispense point. Opening the valve allows process fluid to flow at the point of dispense. A programmable controller operates the pumps and valves. All surfaces within the pumping mechanism, lines and valves that touch the process fluid must not react with or contaminate the process fluid. The pumps, containers of process fluid, and associated valving are sometimes stored in a cabinet that also house a controller.
Pumps for these types of systems are typically some form of a positive displacement type of pump, in which the size of a pumping chamber is enlarged to draw in fluid into the chamber, and then reduced to push it out. Types of positive displacement pumps that have been used include hydraulically actuated diaphragm pumps, bellows type pumps, piston actuated, rolling diaphragm pumps, and pressurized reservoir type pumping systems. U.S. Pat. No. 4,950,134 (Bailey et al.) is an example of a typical pump. It has an inlet, an outlet, a stepper motor and a fluid displacement diaphragm. When the pump is commanded electrically to dispense, the outlet valve opens and the motor turns to force flow of a displacement or actuating fluid into the actuating fluid chamber, resulting in the diaphragm moving to reduce the size the pumping chamber. Movement of the diaphragm forces process fluid out the pumping chamber and through the outlet valve.
Due to concerns over contamination, current practice in the semiconductor manufacturing industry is to use a pump only for pumping a single type of processing fluid or “chemistry.” In order to change chemistries being pumped, all of the surfaces contacting the processing fluid have to be changed. Depending on the design of the pump, this tends to be cumbersome and expensive, or simply not feasible. It is not uncommon to see processing systems that use up to 50 pumps in today's fabrication facilities.
A dispensing apparatus that supplies process chemicals from different sources is shown in U.S. Pat. No. 6,797,063 (Mekias). Here, the dispensing apparatus has two or more process chambers inside of a control chamber. The volume of the process chambers increases or decreases by adding control fluid to or removing control fluid from the control chamber. The use of valving at the inlets and outlets of the process chambers, in combination with a pressurized fluid reservoir that controls fluid into and out of the control chamber controls the flow of dispensed fluid through the process chambers.